Astrocytes play a fundamental role in signaling, maintenance and protection of the brain. Data generated in the sponsor's laboratory suggest that the neuroprotective ability of astrocytes diminishes with age. It was also discovered that the purinergic receptor (P2Y-R) signaling pathway in cultured astrocytes significantly increases the resistance of astrocytes and neurons to oxidative stress. This stimulated protective mechanism decreased during aging, but remarkably, its magnitude was greater in old astrocytes when compared to non- stimulated young astrocytes. P2Y-R-enhanced neuroprotection in vitro appears to depend on increased release of glutathione (GSH) from astrocytes. Our data also indicate enhanced neuroprotection depends on astrocyte mitochondrial ATP stimulation. These data were obtained in vitro, which could alter the cell physiology. Therefore the focus of this proposal is to determine the role of GSH production in astrocyte neuroprotection in vivo using whole brain, small animal imaging, and behavioral measures in young and old animals. The long-term goal of this proposal is to understand the role of astrocytes in the maintenance and protection of the brain during aging. The overall hypothesis is that neuroprotection can be enhanced by increasing mitochondrial ATP levels and GSH production in astrocytes at anytime during the aging process. To test the hypothesis, the following Specific Aims are proposed: 1) To delineate the in vivo role of astrocyte GSH production in P2Y-R enhanced neuroprotection during ischemia/reperfusion in the aging brain, and 2) To non-invasively investigate the role of P2Y-R enhanced neuroprotection following ischemia/reperfusion in the aging brain. Relevance: Accumulation of oxidative damage to astrocytes is likely to degrade their supportive and neuroprotective functions and significantly contribute to the aging process. Data collected from this research will help to identify and characterize novel protective pathways in astrocytes that can be activated to protect the brain during aging. These pathways should also serve as attractive therapeutic targets to address many neuropathological processes, including stroke and dementias.